Polymers having functional groups at the chain ends can be cured by themselves or with the help of an adequate curing agent to give cross-linked materials with high heat resistance and durability. Representative examples are the polymers having alkenyl groups or curable silyl groups at the chain ends. A polymer having alkenyl groups at the chain ends can be cured using a polyvalent hydrogensilicon compound as a curing agent or by photopolymerization. A polymer having curable silyl groups can be cured by absorbing moisture in the presence of an adequate condensation catalyst to give a cross-linked material.
Some examples of the main chain structure of these polymers are the polyether polymers such as polyethylene oxide, polypropylene oxide and polytetramethylene oxide; the hydrocarbon polymers such as polybutadiene, polyisoprene, polychloroprene, polyisobutylene and their hydrogenated derivatives; the polyester polymers such as polyethylene terephthalate, polybutyleneterephthalate and polycaprolactone. These polymers are being used for many applications based on their main chain structure and curing system.
The polymers exemplified as above are prepared by ionic polymerization or polycondensation. On the other hand, vinyl polymers having functional groups at the chain ends, which may be prepared by radical polymerization, are rarely commercialized. Among vinyl polymers, (meth)acrylic polymers exhibit excellent physical properties such as high weatherability and clarity, which properties can not be obtained from the aforementioned polyether polymers, hydrocarbon polymers and polyester polymers. Due to those properties, (meth)acrylic polymers possessing alkenyl groups or curable silyl groups at the side chains are being used for high weatherability paints.
(Meth)acrylic polymers having alkenyl or curable silyl groups at the chain ends would impart to the cross-linked material with better mechanical properties than obtained with (meth)acrylic polymers with such functional groups at their side chains. Considerable efforts have been made so far to develop a method to synthesize such polymers, however, their commercial production has yet to be reached.
Unexamined Japanese Patent Publication No.5-255415 (1993) discloses a synthetic method for the preparation of (meth)acrylic polymers having alkenyl groups at both ends using an alkenyl group-containing disulfide compound as a chain transfer agent. Unexamined Japanese Patent Publication No.5-262808 (1993) also discloses a synthetic method for (meth)acrylic polymers having alkenyl groups at both ends via (meth)acrylic polymers with a hydroxyl group at both ends, which in turn, are prepared using a large excess of a hydroxyl group-containing disulfide compound as a chain transfer agent. However, it is difficult to introduce alkenyl groups onto both chain ends of the polymers in a high functionality ratio by these methods.
On the other hand, Unexamined Japanese Patent Publication No.59-168014 (1984) discloses a synthetic method for (meth)acrylic polymers having curable silyl groups at both ends using a curable silyl group-containing disulfide compound as a chain transfer agent. Unexamined Japanese Patent Publication No.61-133201 (1986) also discloses a method for the preparation of (meth)acrylic polymers using a curable silyl group-containing hydrogensilicon compound or a halosilane compound as a chain transfer agent. However, it is also difficult to introduce curable silyl groups onto both chain ends of the polymers in a high functionality ratio by these methods.
The object of the present invention is to provide methods for the preparation of (meth)acrylic polymers having alkenyl groups or curable silyl groups at the chain ends in a higher functionality ratio than those obtained by the conventional methods, and also provides curable compositions containing those polymers.
Recently, new living radical polymerization methods were developed and made possible the synthesis of (meth)acrylic polymers having halogen atoms at the chain ends in a high ratio (see: Matyjaszewski et al, J. Am. Chem. Soc. 1995, 117, 5614; Macromolecules 1995, 28, 7901; Science 1996, 272, 866; Sawamoto et al, Macromolecules 1995, 28, 1721).
The present inventors have found that (meth)acrylic polymers having alkenyl groups or curable silyl groups at the chain ends in a high functionality ratio can be obtained by using the above living radical polymerization method.